This invention relates to an optical memory device disclosed in a separate U.S. patent application by the applicant, titled MEMORY DEVICE, Ser. No. 06/392,147, filed June 25, 1982, now U.S. Pat. No. 4,532,608.
The memory device comprises a substrate having a plurality of void cells with empty spaces. Each void contains a certain amount of ablative material deposited on its wall. The substrate is transparent to the light used for reading and writing of the information. The cells, or bubbles, with empty spaces of certain shape, are embedded in the substrate. The ablative material is opaque to the light used for reading and writing of the information. The ablative material can be vaporized by a high intensity light beam during a write operation.
The distribution of the ablative material on the cell wall determines the content of the information stored. During a read operation, a low intensity light beam is directed towards the cell to detect the pattern of distribution of the ablative material. During a write operation, a high intensity light beam is directed towards the cell to vaporize and redistribute the ablative material.
In one embodiment of the memory device, a cell is used to store one bit of information. The cell is made in an elongated shape with its middle slightly constricted. When a bit of information is stored, one end of the cell has the ablative material covering its wall and the other end is clear of the ablative material. A binary one or zero is stored depending on which end is covered or clear. To read the information, a low intensity light beam is directed towards one particular end of the cell. A light sensor downstream of the light beam is used to detect the content of the information. To change the content of the information previously stored, a high intensity light beam is directed towards the end covered with ablative material. The light beam is of sufficient intensity so that the ablative material is vaporized. The vaporized material diffuses to the other end and is then allowed to cool down and deposit on its wall. As a result, a binary zero is changed to a one or vice versa. FIG. 1 illustrates such an embodiment. A substrate 21 is made as a plate. A cut on the plate exposes one half of a cell. The cell has two ends 23 and 24 joined by a narrower section. The two ends represent the numbers 0 and 1. If the end 23 is clear and the end 24 is covered, the number 0 is stored. If the end 24 is clear and the end 23 is covered, the number 1 is stored. A light beam 22 is shown directed towards the lower end of the cell. The plate in this figure is shown facing the left.
This invention discloses a method for making the memory device of the type disclosed.
An important property of a mass memory device is its ability to store a large amount of information in a given surface area of the recording medium. To achieve a high density of information in the memory device refered to above, small cell size is required. A suitable amount of ablative material should also be sealed in each cell. An object of this invention is to disclose a method for making the memory device with small cells and with controllable amounts of ablative material sealed in them. Another object is to make the memory device with cells of desirable shape and at preselected locations. Still another object of the invention is to disclose a method that is suitable for mass production of the memory device.